1. Field of the Invention
In some high temperature applications, for example, rocket nozzles, turbines or bearings, there is a need for materials which have high resistance to ablation, erosion, and thermal shock. While woven carbon-carbon composites have excellent ablation and thermal shock resistance, their erosion resistance is poor. Alternatively, carbides have excellent erosion resistance but poor ablation and thermal shock resistance.
The prior art shows that hot pressed carbide-graphite composites can be formed from blends of carbide and graphite powders and do have improved properties over the individual constituents, i.e., carbide or graphite. For many applications, however, further improvement of the thermal shock resistance is a necessity. Filaments which reinforce woven bodies would improve the hot press powder constituent bodies but filaments up to now have been very difficult to distribute uniformly by blending with the individual carbide or graphite powders.
2. Prior Art
1. U.S. Pat. No. 3,369,920, Bourdeau et al., describes a process for depositing pyrolytic coatings on carbon and graphite filaments by depositing said coatings at a temperature between 1300.degree. and 2100.degree. C. at a pressure of less than 100 millimeters of mercury using a diluent gas, said gas selected from the group consisting of the hydrocarbons and halides of tantalum, zirconium, niobium, hafnium, tungston, silicon, and boron. The composite material of this patent is formed at high temperatures, i.e., 1300.degree.-2100.degree. C., while applicants' method is directed to the depositing of a tantalum metal on a graphite cloth at a temperature in the range of 650.degree. to 900.degree. C. The temperature is a critical limitation of applicants' process since at temperatures beyond 900.degree. C. the coating atmosphere attacks or degrades the graphite cloth. In addition, the composite of the Bourdeau patent is not fully dense and as a consequence does not have the high strength of applicants' composite.
2. U.S. Pat. No. 3,294,880, Michael Turkat, describes a method of forming continuous lengths of a pure crystalline filament of pyrolytic graphite, pyrolytic carbides, and combinations thereof by cracking hydrocarbon gases in a vacuum furnace at temperatures in the range of 1900.degree. to 2300.degree. C., and depositing the decomposition products thereof on said filament. In contrast, the graphite of applicants' process is not isotropic and hence is less susceptible to stress failures experienced with a pyrolytic graphite-carbide composite.